EP0752267A2

EP0752267A2 - A diamond sintered compact and a process for the production of the same

Info

Publication number: EP0752267A2
Application number: EP96305018A
Authority: EP
Inventors: Hitoshi Itami Works of Sumitomo Elec. Ind Sumiya; Shuichi Itami Works of Sumitomo Elec. Ind. Satoh
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1995-07-07
Filing date: 1996-07-08
Publication date: 1997-01-08
Also published as: US5769176A; EP0752267A3

Abstract

The present invention provides a diamond sintered compact having a higher strength as well as better heat, breakage and corrosion resistance than the compacts of the prior art, which can thus be effectively applied to tool materials for cutting or polishing non-ferrous metals or ceramics, and to edge materials for drill bits for petroleum excavation. The diamond sintered compact comprises 0.1 to 30 volume % of at least one compound which comprises oxygen and at least one element selected from silicon and titanium, and the balance of diamond, for example, a titanate of a metal selected from iron, cobalt, nickel and manganese.

Description

The present invention relates to a diamond sintered body or compact, a process for the production of the same and a tool for cutting or excavating using the diamond sintered body.
The diamond sintered body of the present invention is preferably applied to tool materials for cutting or polishing non-ferrous metals or ceramics, and for edge materials of drill bits for petroleum excavation, etc.
As diamond sintered compacts, it is known to use, as a sintering agent or binder, iron group metals, such as Co, Ni and Fe or ceramics, such as SiC. Such compacts have found application commercially in cutting tools for non-ferrous metals and in tool bits for excavation.
Diamond sintered compacts relying on carbonate sintering agents are also known (Japanese Patent Laid-Open Publication Nos. 74766/1992 and 114966/1992).
Additionally, natural diamond sintered compacts (carbonado) exist. These are not, however, used commercially because their origin is not clear, their quality is variable and their output is low.
A diamond sintered compact using an iron group metal such as Co, functioning as a catalyst capable of accelerating graphitization of diamond, has poor heat resistance, since the diamond is graphitized at about 700 °C in an inert gas atmosphere. Moreover, this sintered compact does not have a high strength and tends to be rather fragile due to the presence of the metal, as a continuous phase, in the grain boundaries of the diamond grains. Furthermore, there is a problem with thermal deterioration due to the difference in thermal expansion between the metal and the diamond.
In order to raise the heat resistance, it has been proposed to remove the metal in the above described grain boundaries by an acid treatment. By such a treatment, the heat resistance temperature is increased to about 1200 °C, but the strength is reduced considerably (by about 30 %) because the sintered body becomes porous.
Diamond sintered bodies which rely on SiC binder materials exhibit excellent heat resistance, but have low strengths due to the absence of binding between the diamond grains.
Diamond sintered compacts featuring carbonate sintering agents also exhibit excellent heat resistance compared with Co binders, but have lower strengths, since the carbonate starts to decompose at about 1000 °C. Furthermore, the compacts cannot be used in applications where an acid environment exists, for example some of the environments in which excavating bits are used, because the carbonate is readily dissolved.
It is an object of the present invention to provide a diamond sintered compact having excellent breakage resistance, heat resistance and acid resistance, and a process for the production of the same, whereby the above described problems of the prior art can be addressed.
It is another object of the present invention to provide a tool for cutting, polishing or excavating using the diamond sintered compact.
These objects can be attained by a diamond sintered compact comprising 0.1 to 30 volume % of at least one of compounds containing silicon and/or titanium and oxygen and the balance of diamond, for example, a diamond sintered compact comprising 0.1 to 30 volume % of a material consisting of a compound containing at least one metal selected from the group consisting or iron, cobalt, nickel and manganese, titanium and oxygen, and the balance of diamond.
The inventors have made various efforts to solve the problems of the prior art and develop a diamond sintered compact having high strength as well as excellent heat resistance, breakage resistance, wear resistance and corrosion resistance, which can be synthesized at relatively moderate conditions and consequently, have reached the present invention.
Preferred embodiments of the present invention will now be illustrated in detail.
The first embodiment of the present invention consists in (1) a diamond sintered compact comprising 0.1 to 30 volume % of a material consisting of a compound containing at least one metal selected from the group consisting of iron, cobalt, nickel and manganese, titanium and oxygen, and the balance of diamond, in particular, including (2) the diamond sintered compact as described in above (1), wherein the compound containing at least one metal selected from the group consisting of iron, cobalt, nickel and manganese, titanium and oxygen is a titanate of a metal selected from the group consisting of iron, cobalt, nickel and manganese and (3) the diamond sintered compact as described in above (1), wherein the compound containing at least one metal selected from the group consisting of iron, cobalt, nickel and manganese, titanium and oxygen is a composite oxide or solid solution consisting of an oxide of a metal selected from the group consisting of iron, cobalt, nickel and manganese, and titanium oxide.
In addition, there are provided (4) a process for the production of the diamond sintered compact as described in any one of above (1) to (3), which comprises using a titanate of a metal selected from the group consisting of iron, cobalt, nickel and manganese, as a sintering agent, mixing a powder of the titanate with diamond powder, non-diamond carbon powder or mixed powders of diamond and non-diamond carbon, and maintaining and sintering the mixture under pressure and temperature conditions in the thermodynamically stable region of diamond, (5) a process for the production of the diamond sintered compact as described in any one of above (1) to (3), which comprises using a titanate of a metal selected from the group consisting of iron, cobalt, nickel and manganese, and titanium oxide, as a sintering agent, laminating a shaped body of this powder and a shaped body of diamond powder, shaped body of non-diamond carbon powder or shaped body of mixed powders of diamond and non-diamond carbon, and maintaining and sintering the laminate under pressure and temperature conditions in the thermodynamically stable region of diamond and (6) the process for the production of the diamond sintered compact as described in any one of above (4) or (5), wherein a mixture of an oxide of a metal selected from the group consisting of iron, cobalt, nickel and manganese, and titanium oxide is used as a sintering agent in place of the titanate.
In each of these production processes, the sintering agent is added to the raw material powder so that it is present in a proportion of 0.1 to 30 volume % in the composition.
The second embodiment of the present invention consists in (1) a diamond sintered compact comprising 0.1 to 30 volume % of a material consisting of a compound containing titanium, at least one metal selected from the group consisting of alkali metals and alkaline earth metals, and oxygen, and the balance of diamond, in particular, including (2) the diamond sintered compact as described in above (1), wherein the compound containing titanium, at least one metal selected from the group consisting of alkali metals and alkaline earth metals, and oxygen is a titanate of a metal selected from the group consisting of alkali metals and alkaline earth metals and (3) the diamond sintered compact as described in above (1), wherein the compound containing titanium, at least one metal selected from the group consisting of alkali metals and alkaline earth metals, and oxygen is a composite oxide or solid solution consisting of an oxide of a metal selected from the group consisting of alkali metals and alkaline earth metals and titanium oxide.
In addition, there are provided (4) a process for the production of the diamond sintered compact as described in any one of above (1) to (3), which comprises using a titanate of a metal selected from the the group consisting of alkali metals and alkaline earth metals, as a sintering agent, mixing a powder of the titanate with diamond powder, non-diamond carbon powder or mixed powders of diamond and non-diamond carbon, and maintaining and sintering the mixture under pressure and temperature conditions in the thermodynamically stable region of diamond, (5) a process for the production of the diamond sintered compact as described in any one of above (1) to (3), which comprises using a titanate of a metal selected from the the group consisting of alkali metals and alkaline earth metals, as a sintering agent, laminating a shaped body of this powder and a shaped body of diamond powder, shaped body of non-diamond carbon powder or shaped body of mixed powders of diamond and non-diamond carbon, and maintaining and sintering the laminate under pressure and temperature conditions in the thermodynamically stable region of diamond and (6) the process for the production of the diamond sintered compact as described in above (4) or (5), wherein a mixture of an oxide of a metal selected fromthe group consisting of alkali metals and alkaline earth metals, and titanium oxide is used as the sintering agent in place of the titanate.
In each of these production processes, the sintering agent is added to the raw material powder so that it is present in a proportion of 0.1 to 30 volume % in the composition.
The third embodiment of the present invention consists in (1) a diamond sintered compact comprising 0.1 to 30 volume % of a material consisting of a compound containing a rare earth element, titanium and oxygen, and the balance of diamond, in particular, including (2) the diamond sintered compact as described in above (1), wherein the compound containing a rare earth element, titanium and oxygen is a titanate of a rare earth element and (3) the diamond sintered compact as described in above (1), wherein the compound containing a rare earth element, titanium and oxygen is a composite oxide or solid solution consisting of an oxide of a rare earth element and titanium oxide.
In addition, there are provided (4) a process for the production of the diamond sintered compact as described in any one of above (1) to (3), which comprises using a titanate of a rare earth element as a sintering agent, mixing a powder of the titanate with diamond powder, non-diamond carbon powder or mixed powders of diamond and non-diamond carbon, and maintaining and sintering the mixture under pressure and temperature conditions in the thermodynamically stable region of diamond, (5) a process for the production of the diamond sintered compact as described in any one of above (1) to (3), which comprises using a titanate of a rare earth element as a sintering agent, laminating a shaped body of this powder and a shaped body of diamond powder, shaped body of non-diamond carbon powder or shaped body of mixed powders of diamond and non-diamond carbon, and maintaining and sintering the laminate under pressure and temperature conditions in the thermodynamically stable region of diamond, and (6) the process for the production of the diamond sintered compact as described in above (4) or (5), which comprises using a mixture of an oxide of a rare earth element and titanium oxide, as another sintering agent.
In each of these production processes, the sintering agent is added to the raw material powder so that it is present in a proportion of 0.1 to 30 volume % in the composition.
The fourth embodiment of the present invention consists in (1) a diamond sintered compact comprising 0.1 to 30 volume % of a material consisting of a compound containing an alkaline earth metal, silicon and oxygen, and the balance of diamond, in particular, including (2) the diamond sintered compact as described in above (1), wherein the compound containing an alkaline earth metal. silicon and oxygen is a silicate of an alkaline earth metal and (3) the diamond sintered compact as described in above (1), wherein the compound containing an alkaline earth metal, silicon and oxygen is a composite oxide or solid solution consisting of an oxide of an alkaline earth metal and silicon oxide.
In addition, there are provided (4) a process for the production of the diamond sintered compact as described in any one of above (1) to (3), which comprises using a silicate of an alkaline earth metal as a sintering agent, mixing a powder of the silicate with diamond powder, non-diamond carbon powder or mixed powders of diamond and non-diamond carbon, and maintaining and sintering the mixture under pressure and temperature conditions in the thermodynamically stable region of diamond, (5) a process for the production of the diamond sintered compact as described in any one of above (1) to (3), which comprises using a silicate of an alkaline earth metal as a sintering agent, laminating a shaped body of this powder and a shaped body of diamond powder, shaped body of non-diamond carbon powder or shaped body of mixed powders of diamond and non-diamond carbon, and maintaining and sintering the laminate under pressure and temperature conditions in the thermodynamically stable region of diamond, and (6) the process for the production of the diamond sintered compact as described in above (4) or (5), wherein the mixture of an oxide of an alkaline earth metal and silicon oxide is used as the sintering agent in place of the silicate.
In each of these production processes, the sintering agent is added to the raw material powder so that it is present in a proportion of 0.1 to 30 volume % in the composition.
The fifth embodiment of the present invention consists in (1) a diamond sintered compact comprising 0.1 to 30 volume % of a material consisting of a compound containing a rare earth element, silicon and oxygen, and the balance of diamond, in particular, including (2) the diamond sintered compact as described in above (1), wherein the compound containing a rare earth element, silicon and oxygen is a silicate of a rare earth element and (3) the diamond sintered compact as described in above (1), wherein the compound containing a rare earth element, silicon and oxygen is a composite oxide or solid solution consisting of an oxide of a rare earth element and silicon oxide.
In addition, there are provided (4) a process for the production of the diamond sintered compact as described in any one of above (1) to (3), which comprises using a silicate of a rare earth element as a sintering agent, mixing a powder of the silicate with diamond powder, non-diamond carbon powder or mixed powders of diamond and non-diamond carbon, and maintaining and sintering the mixture under pressure and temperature conditions in the thermodynamically stable region of diamond, (5) a process for the production of the diamond sintered compact as described in any one of above (1) to (3), which comprises using a silicate of a rare earth element as a sintering agent, laminating a shaped body of this powder and a shaped body of diamond powder, shaped body of non-diamond carbon powder or shaped body of mixed powders of diamond and non-diamond carbon, and maintaining and sintering the laminate under pressure and temperature conditions in the thermodynamically stable region of diamond, and (6) the process for the production of the diamond sintered compact as described in above (4) or (5), wherein a mixture of an oxide of a rare earth element and silicon oxide is used as the sintering agent in place of the silicate.
In each of these production processes, the sintering agent is added to the raw material powder so that it is present in a proportion of 0.1 to 30 volume % in the composition.
The sixth embodiment of the present invention consists in (1) a diamond sintered compact comprising 0.1 to 30 volume % of a material consisting of a compound containing silicon, titanium and oxygen, and the balance of diamond, in particular, including (2) the diamond sintered compact as described in above (1), wherein the compound containing silicon, titanium and oxygen is a a composite oxide or solid solution consisting of silicon oxide and titanium oxide.
In addition, there are provided (3) a process for the production of the diamond sintered compact as described in above (1) or (2), which comprises using a mixture of silicon oxide and titanium oxide, as a sintering agent, mixing a powder of the mixture with diamond powder, non-diamond carbon powder or mixed powders of diamond and non-diamond carbon, and maintaining and sintering the mixture under pressure and temperature conditions in the thermodynamically stable region of diamond, (4) a process for the production of the diamond sintered compact as described in above (1) or (2), which comprises using a mixture of silicon oxide and titanium oxide, laminating a shaped body of this powder and a shaped body of diamond powder, shaped body of non-diamond carbon powder or shaped body of mixed powders of diamond and non-diamond carbon, and maintaining and sintering the laminate under pressure and temperature conditions in the thermodynamically stable region of diamond, (5) the process for the production of the diamond sintered compact as described in above (3) or (4), wherein the mixture of silicon oxide and titanium oxide used as a sintering agent contains the titanium oxide in a proportion of 0.1 to 50 volume % and (6) the process for the production of the diamond sintered compacts as described in any one of above (3) to (5), wherein the silicon oxide contained in the mixture of silicon oxide and titanium oxide used as a sintering agent is silicic acid or silicon oxide hydrate.
In each of these production processes, the sintering agent is added to the raw material powder so that it is present in a proportion of 0.1 to 30 volume % in the composition.
The feature of the present invention consists in a diamond sintered compact comprising 0.1 to 30 volume % of at least one of compounds containing silicon and/or titanium and oxygen and the balance of diamond, and above all, the first embodiment comprises using, as a sintering agent for the diamond sintered compact, a titanate of a metal selected from the group consisting of iron, cobalt, nickel and manganese or a mixture of an oxide of a metal selected from the group consisting of iron, cobalt, nickel and manganese with titanium oxide.
Up to the present time, no examples have been known as to using, as an effective sintering agent for the diamond sintered compact, a titanate of a metal selected from the group consisting of iron, cobalt, nickel and manganese or a mixture of an oxide of a metal selected from the group consisting of iron, cobalt, nickel and manganese with titanium oxide. The inventors have now found that a diamond sintered compact having a higher strength as well as more excellent breakage resistance, heat resistance, wear resistance and corrosion reistance, having hitherto not been given, can be obtained by using these materials as a sintering agent.
Examples of the titanate of a metal selected from the group consisting of iron, cobalt, nickel and manganese include FeTiO₃, FeTi₂O₅, CoTiO₃, MnTiO₃, NiTiO₃, etc. These materials are capable of exhibiting a strong catalytic function for diamond and when using them as a sintering agent, there is formed a matrix consisting of diamond grains very strongly bonded with each other. Furthermore, abnormal grain growth hardly takes place to result in a sintered compact with homogeneous structure. Consequently, a diamond sintered compact having a higher strength as well as more excellent breakage resistance and wear resistance, having hitherto not been given, can be obtained. Such a sintering agent has preferably a grain diameter range of 0.01 to 10 µm.
The diamond sintered body obtained in this way has a feature of containing a material consisting of a compound containing a metal selected from the group consisting of iron, cobalt, nickel and manganese, illustrative of which are titanates of iron or cobalt, composite oxides or solid solutions of oxides such as iron oxides and cobalt oxides with titanium oxides. These materials are stable at a high temperature, e.g. about 1300 °C and resistant to acids or alkalies. Accordingly, the diamond sintered compact of the first embodiment of the present invention has very excellent properties for heat resistance and corrosion resistance.
In the diamond sintered compact of the first embodiment of the present invention, the content of a material consisting of a compound containing a metal selected from the group consisting of iron, cobalt, nickel and manganese, titanium and oxygen is present in a proportion of preferably 0.1 to 30 volume %, since if less than 0.1 volume %, the bonding property, i.e. sintering property among diamond grains is degraded, while if more than 30 volume %, the strength and wear resistance are lowered due to the presence of excessive titanium oxide.
As raw materials, there can be used synthetic diamond powders, natural diamond powders, polycrystalline diamond powders, etc. The grain diameter of the powder is generally in a range of 0.01 to 200 µm and depending upon uses thereof, there are used those whose grain diamters are adjusted to fine or coarse or mixtures of fine grains and coarse grains.
In place of these diamonds, non-diamond carbons such as graphite, glassy carbons, pyrolytic graphites, etc. can be used as the raw material. A mixture of diamond and non-diamond graphite can also be used.
For the production of a diamond sintered compact according to the first embodiment of the present invention, there are processes comprising maintaining a mixture of diamond powder or non-diamond carbon powder with a titanate of iron or cobalt or a mixture of iron oxide or cobalt oxide and titanium oxide under pressure and temperature conditions in the thermodynamically stable region of diamond and comprising laminating a shaped body of diamond powder or non-diamond graphite powder and a shaped body of a titanate of iron or cobalt or a mixture of iron oxide or cobalt oxide with titanium oxide, maintaining and sintering the laminate under pressure and temperature conditions in the thermodynamically stable region of diamond,
In a method of mixing a raw material with a sintering agent, the raw material and sintering agent are mechanically mixed by dry or wet process and the resulting powder is compressed and molded or charged in a capsule of Mo, etc., followed by sintering at a high pressure and temperature. Even if the raw material powder is of fine grains, the sintering agent can uniformly be dispersed therein and a diamond sintered compact having a thick shape can be produced. For example, this method is suitable for the production of a cutting tool (fine grain sintered compact) needing a well finished surface or a sintered compact needing a thick shape such as dies. In the case of using a raw material of coarse grain, however, it is considerably difficult to uniformly mix a sintering agent.
In a method of laminating and arranging a raw material and sintering agent, on the other hand, plate-shaped bodies of the raw material and sintering agent are respectively prepared, laminated to be contacted with each other and then subjected to a high pressure and high temperature treatment, during which the sintering agent is diffused and impregnated into the raw material layer and diamond grains are sintered. According to this method, the sintering agent can uniformly be added even when using a coarse grain raw material, so a diamond sintered compact with a higher strength and higher wear resistance can stably be obatined and this is suitable for the production of a sintered compact such as wear resistance tools, drill bits, etc.
The second embodiment of the present invention comprises using, as a sintering agent for the diamond sintered compact, a titanate of an alkali metal or alkaline earth metal or a mixture of an oxide of an alkali metal or alkaline earth metal and titanium oxide.
Up to the present time, no examples have been known as to using, as an effective sintering agent for the diamond sintered compact, a titanate of an alkali metal or alkaline earth metal or a mixture of an oxide of an alkali metal or alkaline earth metal and titanium oxide. The inventors have now found that a diamond sintered compact having a higher strength as well as more excellent breakage resistance, heat resistance, wear resistance and corrosion reistance, having hitherto not been given, can be obtained by using, as the sintering agent, a titanate of an alkali metal or alkaline earth metal, or a mixture of an oxide of an alkali metal or alkaline earth metal and titanium oxide.
Examples of the titanate of an alkali metal or alkaline earth metal include LiTiO₃, MgTiO₃, CaTiO₃, SrTiO₃, etc. These materials are capable of exhibiting a strong catalytic function for diamond and when using them as a sintering agent, there is formed a matrix consisting of diamond grains very strongly bonded with each other. Furthermore, abnormal grain growth hardly takes place to result in a sintered compact with homogeneous structure. Consequently, a diamond sintered compact having a higher strength as well as more excellent breakage resistance and wear resistance, having hitherto not been given, can be obtained. Such a sintering agent has preferably a grain diameter range of 0.01 to 10 µm.
The diamond sintered body obtained in this way has a feature of containing a material consisting of a compound containing titanium, an alkali metal or alkaline earth metal and oxygen, illustrative of which are titanates of alkali metals or alkaline earth metals, as described above, or composite oxides or solid solutions of alkali metal oxides or alkaline earth metal oxides with titanium oxides. These materials are stable at a high temperature, e.g. about 1500 °C and resistant to acids or alkalies. Accordingly, the diamond sintered compact of the second embodiment of the present invention has very excellent properties for heat resistance and corrosion resistance.
In the diamond sintered compact of the second embodiment of the present invention, the content of a material consisting of a compound containing titanium, an alkali metal or alkaline earth metal and oxygen is present in a proportion of preferably 0.1 to 30 volume %, since if less than 0.1 volume %, the bonding property, i.e. sintering property among diamond grains is degraded, while if more than 30 volume %, the strength and wear resistance are lowered due to the presence of excessive titanium oxide.
As raw materials, there can be used synthetic diamond powders, natural diamond powders, polycrystalline diamond powders, etc. The grain diameter of the powder is generally in a range of 0.01 to 200 µm and depending upon uses thereof, there are used those whose grain diamters are adjusted to fine or coarse or mixtures of fine grains and coarse grains.
In place of these diamonds, non-diamond carbons such as graphite, glassy carbons, pyrolytic graphites, etc. can be used as the raw material. A mixture of diamond and non-diamond graphite can also be used.
For the production of a diamond sintered compact according to the second embodiment of the present invention, there are processes comprising maintaining a mixture of diamond powder or non-diamond carbon powder with a titanate of an alkali metal or alkaline earth metal, or a mixture of an alkali metal oxide or alkaline earth metal oxide and titanium oxide under pressure and temperature conditions in the thermodynamically stable region of diamond and comprising laminating a shaped body of diamond powder or non-diamond graphite powder and a shaped body of a titanate of an alkali metal or alkaline earth metal or a mixture of alkali metal oxide or alkaline earth metal oxide with titanium oxide, maintaining and sintering the laminate under pressure and temperature conditions in the thermodynamically stable region of diamond.
The method of mixing a raw material with a sintering agent and the method of laminating and arranging a raw material and a sintering agent can be carried out in the similar manner to those in the first embodiment of the present invention with the equal benefits thereto.
The third embodiment of the present invention comprises using, as a sintering agent for the diamond sintered compact, a titanate of a rare earth element or a mixture of an oxide of a rare earth element with titanium oxide.
Up to the present time, no examples have been known as to using, as an effective sintering agent for the diamond sintered compact, a titanate of a rare earth element or a mixture of an oxide of a rare earth element with titanium oxide. The inventors have now found that a diamond sintered compact having a higher strength as well as more excellent breakage resistance, heat resistance, wear resistance and corrosion reistance, having hitherto not been given, can be obtained by using, as the sintering agent, a titanate of a rare earth element or a mixture of an oxide of a rare earth element with titanium oxide.
Examples of the titanate of a rare earth element include M₂TiO₅ or M₂Ti₂O₇ wherein M is a rare earth element. The rare earth element includes scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), prometium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytteribium (Yb), and lutetium (Lu).
Examples of the oxide of a rare earth element include M₂O₃ or MO₂ wherein M is a rare earth element. The titanate of a rare earth element or a mixture of an oxide of a rare earth element and titanium oxide is capable of exhibiting a strong catalytic function for diamond and when using them as a sintering agent, there is formed a matrix consisting of diamond grains very strongly bonded with each other. Furthermore, abnormal grain growth hardly takes place to result in a sintered compact with homogeneous structure. Consequently, a diamond sintered compact having a higher strength as well as more excellent breakage resistance and wear resistance, having hitherto not been given, can be obtained.
The diamond sintered body obtained in this way has a feature of containing a material consisting of a compound containing a rare earth element, titanium, and oxygen, illustrative of which are titanates of rare earth elements or composite oxides or solid solutions of oxides of rare earth elements and titanium oxides, as described above. These materials are stable at a high temperature, e.g. about 1300 °C and resistant to acids or alkalies. Accordingly, the diamond sintered compact of the third embodiment of the present invention has very excellent properties for heat resistance and corrosion resistance.
In the diamond sintered compact of the third embodiment of the present invention, the content of a material consisting of a compound containing a rare earth element, titanium and oxygen is present in a proportion of preferably 0.1 to 30 volume %, since if less than 0.1 volume %, the bonding property, i.e. sintering property among diamond grains is degraded, while if more than 30 eolume %, the strength and wear resistance are lowered due to the presence of excessive titanium oxide.
As raw materials, there can be used synthetic diamond powders, natural diamond powders, polycrystalline diamond powders, etc. The grain diameter of the powder is generally in a range of 0.01 to 200 µm and depending upon uses thereof, there are used those whose grain diamters are adjusted to fine or coarse or mixtures of fine grains and coarse grains.
In place of these diamonds, non-diamond carbons such as graphite, glassy carbons, pyrolytic graphites, etc. can be used as the raw material. A mixture of diamond and non-diamond graphite can also be used.
For the production of a diamond sintered compact according to the third embodiment of the present invention, there are processes comprising maintaining a mixture of diamond powder or non-diamond carbon powder with a titanate of a rare earth element or a mixture of an oxide of rare earth element and titanium oxide under pressure and temperature conditions in the thermodynamically stable region of diamond and comprising laminating a shaped body of diamond powder or non-diamond graphite powder and a shaped body of a titanate of a rare earth element or a mixture of an oxide of a rare earth element with titanium oxide, maintaining and sintering the laminate under pressure and temperature conditions in the thermodynamically stable region of diamond.
The method of mixing a raw material with a sintering agent and the method of laminating and arranging a raw material and a sintering agent can be carried out in the similar manner to those in the first embodiment of the present invention with the equal benefits thereto.
The fourth embodiment of the present invention comprises using, as a sintering agent for the diamond sintered compact, a silicate of an alkaline earth metal or a mixture of an oxide of an alkaline earth metal and silicon oxide.
Up to the present time, no examples have been known as to using, as an effective sintering agent for the diamond sintered compact, a silicate of an alkaline earth metal or a mixture of an oxide of an alkaline earth metal and silicon oxide. The inventors have now found that a diamond sintered compact having a higher strength as well as more excellent breakage resistance, heat resistance, wear resistance and corrosion reistance, having hitherto not been given, can be obtained by using, as the sintering agent, a silicate of an alkaline earth metal, or a mixture of an oxide of an alkaline earth metal and silicon oxide.
Examples of the silicate of an alkaline earth metal include MgSiO₃, Mg₂SiO₄, Mg₂Si₃O₈, CaSiO₃, Ca₂SiO₄, BaSi₂O₅, Ba₂Si₃O₈, etc.
The silicate of an alkaline earth element or a mixture of an oxide of an alkaline earth with silicon oxide is capable of exhibiting a strong catalytic function for diamond and when using them as a sintering agent, there is formed a matrix consisting of diamond grains very strongly bonded with each other. Furthermore, abnormal grain growth hardly takes place to result in a sintered compact with homogeneous structure. Consequently, a diamond sintered compact having a higher strength as well as more excellent breakage resistance and wear resistance, having hitherto not been given, can be obtained.
The diamond sintered body obtained in this way has a feature of containing a material consisting of a compound containing an alkaline earth metal, silicon and oxygen, illustrative of which are silicates of alkaline earth metals, as described above, or composite oxides or solid solutions of alkaline earth metal oxides with silicon oxides. These materials are stable at a high temperature. e.g. about 1300 °C and resistant to acids or alkalies. Accordingly, the diamond sintered compact of the fourth embodiment of the present invention has very excellent properties for heat resistance and corrosion resistance.
In the diamond sintered compact of the fourth embodiment of the present invention, the content of a material consisting of a compound containing an alkaline earth metal, silicon and oxygen is present in a proportion of preferably 0.1 to 30 volume %, since if less than 0.1 volume %, the bonding property, i.e. sintering property among diamond grains is degraded, while if more than 30 volume %, the strength and wear resistance are lowered due to the presence of excessive silicate compound.
As raw materials, there can be used synthetic diamond powders, natural diamond powders, polycrystalline diamond powders, etc. The grain diameter of the powder is generally in a range of 0.01 to 200 µm and depending upon uses thereof, there are used those whose grain diamters are adjusted to fine or coarse or mixtures of fine grains and coarse grains.
In place of these diamonds, non-diamond carbons such as graphite, glassy carbons, pyrolytic graphites, etc. can be used as the raw material. A mixture of diamond and non-diamond graphite can also be used.
For the production of a diamond sintered compact according to the fourth embodiment of the present invention, there are processes comprising maintaining a mixture of diamond powder or non-diamond carbon powder with a silicate of an alkaline earth metal or a mixture of an alkaline earth metal oxide and silicon oxide under pressure and temperature conditions in the thermodynamically stable region of diamond and comprising laminating a shaped body of diamond powder or non-diamond graphite powder and a shaped body of a silicate of an alkaline earth metal or a mixture of alkaline earth metal oxide with silicon oxide, maintaining and sintering the laminate under pressure and temperature conditions in the thermodynamically stable region of diamond.
The method of mixing a raw material with a sintering agent and the method of laminating and arranging a raw material and a sintering agent can be carried out in the similar manner to those in the first embodiment of the present invention with the equal benefits thereto.
The fifth embodiment of the present invention comprises using, as a sintering agent for the diamond sintered compact, a silicate of a rare earth element or a mixture of an oxide of a rare earth element and silicon oxide.
Up to the present time, no examples have been known as to using, as an effective sintering agent for the diamond sintered compact, a silicate of a rare earth element or a mixture of an oxide of a rare earth element and silicon oxide. The inventors have now found that a diamond sintered compact having a higher strength as well as more excellent breakage resistance, heat resistance wear resistance and corrosion resistance, having hitherto not been given, can be obtained by using, as the sintering agent, a silicate of a rare earth element or a mixture of an oxide of a rare earth element and silicon oxide, and thus have reached the present invention.
Examples of the silicate of a rare earth element include, for example, M₂SiO₅ or M₂Si₂O₇ wherein M is a rare earth element. The rare earth element includes scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), prometium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytteribium (Yb) and lutetium (Lu).
Examples of the oxide of a rare earth element include M₂O₃ or MO₂ wherein M is a rare earth element. The silicate of a rare earth element or a mixture of an oxide of a rare earth element and silicon oxide is capable of exhibiting a strong catalytic function for diamond and when using them as a sintering agent, there is formed a matrix consisting of diamond grains very strongly bonded with each other. Furthermore, abnormal grain growth hardly takes place to result in a sintered compact with homogeneous structure. Consequently, a diamond sintered compact having a higher strength as well as more excellent breakage resistance and wear resistance, having hitherto not been given, can be obtained.
The diamond sintered body obtained in this way has a feature of containing a material consisting of a compound containing a rare earth element, silicon and oxygen, illustrative of which are silicates of rare earth elements, as described above, or composite oxides or solid solutions of rare earth element oxides with silicon oxide. These materials are stable at a high temperature, e.g. about 1400 °C and resistant to acids or alkalies. Accordingly, the diamond sintered compact of the fifth embodiment of the present invention has very excellent properties for heat resistance and corrosion resistance.
In the diamond sintered compact of the fifth embodiment of the present invention, the content of a material consisting of a compound containing a rare earth element, silicon and oxygen is present in a proportion of preferably 0.1 to 30 volume %, since if less than 0.1 volume %, the bonding property, i.e. sintering property among diamond grains is degraded, while if more than 30 volume %, the strength and wear resistance are lowered due to the presence of excessive silicate compound.
As raw materials, there can be used synthetic diamond powders, natural diamond powders, polycrystalline diamond powders, etc. The grain diameter of the powder is generally in a range of 0.01 to 200 µm and depending upon uses thereof, there are used those whose grain diamters are adjusted to fine or coarse or mixtures of fine grains and coarse grains.
In place of these diamonds, non-diamond carbons such as graphite, glassy carbons, pyrolytic graphites, etc. can be used as the raw material. A mixture of diamond and non-diamond graphite can also be used.
For the production of a diamond sintered compact according to the fifth embodiment of the present invention, there are processes comprising maintaining a mixture of diamond powder or non-diamond carbon powder with a silicate of a rare earth element or a mixture of an oxide of a rare earth elelment and silicon oxide under pressure and temperature conditions in the thermodynamically stable region of diamond and comprising laminating a shaped body of diamond powder or non-diamond graphite powder and a shaped body of a silicate of a rare earth element or a mixture of an oxide of a rare earth element with silicon oxide, maintaining and sintering the laminate under pressure and temperature conditions in the thermodynamically stable region of diamond.
The method of mixing a raw material with a sintering agent and the method of laminating and arranging a raw material and a sintering agent can be carried out in the similar manner to those in the first embodiment of the present invention with the equal benefits thereto.
The sixth embodiment of the present invention comprises using, as a sintering agent for the diamond sintered compact, a mixture of silicon oxide (SiO₂) and titanium oxide (TiO₂). In place of the silicon oxide, there can be used silicic acids such as H₄SiO₄, H₂SiO₃, H₂Si₂O₂, etc. and hydrates thereof such as SiO₂ · nH₂O.
Up to the present time, no examples have been known as to using, as an effective sintering agent for the diamond sintered compact, a mixture of silicon oxide or silicic acid with titanium oxide. The inventors have now found that a diamond sintered compact having a higher strength as well as more excellent breakage resistance, heat resistance, wear resistance and corrosion resistance, having hitherto not been given, can be obtained by using, as the sintering agent, a mixture of silicon oxide or silicic acid with titanium oxide, and thus have reached the present ivnention.
A mixture of silicon oxide or silicic acid and titanium oxide is capable of exhibiting a strong catalytic function for diamond and when using it as a sintering agent, there is formed a matrix consisting of diamond grains very strongly bonded with each other. Furthermore, abnormal grain growth hardly takes place to result in a sintered compact with homogeneous structure. Consequently, a diamond sintered compact having a higher strength as well as more excellent breakage resistance and wear resistance, having hitherto not been given, can be obtained.
The diamond sintered body obtained in this way has a feature of containing a material consisting of a compound containing silicon, titanium and oxygen, illustrative of which are composite oxides or solid solutions of silicon oxide and titanium oxide. These materials are stable at a high temperature, e.g. about 1500°C and resistant to acids or alkalies. Accordingly, the diamond sintered compact of the sixth embodiment of the present invention has very excellent properties for heat resistance and corrosion resistance.
In the diamond sintered compact of the sixth embodiment of the present invention, the content of a material consisting of a compound containing silicon, titanium and oxygen is present in a proportion of preferably 0.1 to 30 volume %, since if less than 0.1 volume %, the bonding property, i.e. sintering property among diamond grains is degraded, while if more than 30 volume %, the strength and wear resistance are lowered due to the presence of the compound in an excessive amount.
As raw materials, there can be used synthetic diamond powders, natural diamond powders, polycrystalline diamond powders, etc. The grain diameter of the powder is generally in a range of 0.01 to 200 µm and depending upon uses thereof, there are used those whose grain diamters are adjusted to fine or coarse ones or mixtures of fine grains and coarse grains.
In place of these diamonds, non-diamond carbons such as graphite, glassy carbons, pyrolytic graphites, etc. can be used as the raw material. A mixture of diamond and non-diamond graphite can also be used.
For the production of a diamond sintered compact according to the sixth embodiment of the present invention, there are processes comprising maintaining a mixture of diamond powder or non-diamond carbon powder with silicon oxide and titanium oxide under pressure and temperature conditions in the thermodynamically stable region of diamond and comprising laminating a shaped body of diamond powder or non-diamond graphite powder and a shaped body of a mixture of silicon oxide and titanium oxide, maintaining and sintering the laminate, as a raw material, under pressure and temperature conditions in the thermodynamically stable region of diamond.
In this embodiment, the mixture of silicon and titanium oxide preferably contains titanium oxide in a proportion by volume of 0.1 to 50 %. When the proportion of titanium oxide is less than 0.1 % or more than 50 %, the sintering is insufficient and in order to obatin a tenacious sintered compact, very high sintering temperature and pressure conditions, e.g. at least 250 °C and at least 8 GPa are required and production of diamond on a commercial scale is difficult. Moreover, when using silicon oxide alone or titanium oxide alone as a sintering agent, severer pressure and temperature conditions are further required.
In place of the silicon oxide, silicic acids or silicon hydrates can be used. In this case, a tenacious sintered compact can be obtained even if the sintering temperature is somewhat is low.
The method of mixing a raw material with a sintering agent and the method of laminating and arranging a raw material and a sintering agent can be carried out in the similar manner to those in the first embodiment of the present invention with the equal benefits thereto.
The present invention will now be illustrated in detail by the following Examples without limiting the same.

(Example 1)

FeTiO₃ was used as a sintering agent. A synthetic diamond powder with an average grain diameter of 3.5 µm and FeTiO₃ powder with a grain diameter of 1 ∼ 2 µm were respectively and adequately mixed in a proportion of 95 volume % and 5 volume %, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000 °C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 5 volume % of FeTiO₃ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by 7800 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.4 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1200 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Example 2)

Example 1 was repeated except using 5 volume % of CoTiO₃ as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained CoTiO₃ and had a similar hardness, toughness and heat resistance to those of Example 1.

(Example 3)

Example 1 was repeated except using 5 volume % of NiTiO₃ as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained NiTiO₃ and had a similar hardness, toughness and heat resistance to those of Example 1.

(Example 4)

Example 1 was repeated except using 5 volume % of MnTiO₃ as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained MnTiO₃ and had a similar hardness, toughness and heat resistance to those of Example 1.

(Example 5)

Example 1 was repeated except using a mixture of FeO and TiO₂ in a volume ratio of 1 : 1 as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained FeTiO₃ and had a similar hardness, toughness and heat resistance to those of Example 1.

(Example 6)

Example 1 was repeated except using a mixture of CoO and TiO₂ in a volume ratio of 1 : 1 as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained CoTiO₃ and had a similar hardness, toughness and heat resistance to those of Example 1.

(Example 7)

FeTiO₃ was used as a sintering agent. A synthetic diamond powder with an average grain diameter of 15 µm and FeTiO₃ powder with a grain diameter of 1 ∼ 2 µm were respectively shaped in plates with a thickness of 2 mm and 1mm, alternately laminated, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000°C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 2 volume % of FeTiO₃ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by about 8000 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.4 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1200 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Example 8)

FeTiO₃ was used as a sintering agent. A plate-shaped sintered compact of a high purity isotropic graphite with an average grain diameter of 3 µm, having a thickness of 2 mm, and a molded and shaped body of FeTiO₃ powder with a grain diameter of 1 to 2 µm, having a thickness of 1 mm, were alternately laminated, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000 °C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Girdle type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 3 volume % of FeTiO₃ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by about 7800 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.3 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1200 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Comparative Example 1)

FeTiO₃ was used as a sintering agent. Example 1 was repeated except adding a micro amount (about 0.05 volume %) of FeTiO₃ powder with a grain diameter of 1 to 2 µm to a synthetic diamond powder with an average grain diameter of 3.5 µm and adequately mixing them to prepare a raw material, thus obtaining a diamond sinterd compact therefrom. However, the thus obtained sintered compact contained more non-sintered parts.

(Comparative Example 2)

FeTiO₃ was used as a sintering agent. Example 1 was repeated except adding 60 volume % of a synthetic diamond powder with an average grain diameter of 3.5 µm and 40 volume % of FeTiO₃ powder with a grain diameter of 1 to 2 µm and adequately mixing them to prepare a raw material, thus obtaining a diamond sinterd compact therefrom. In the thus obtained sintered compact, however, the grains were not sufficiently bonded with each other to give a low hardness, i.e. about 3500 kg/mm².

(Example 9)

CaTiO₃ was used as a sintering agent. A synthetic diamond powder with an average grain diameter of 3.5 µm and CaTiO₃ powder with a grain diameter of 1 ∼ 2 µm were respectively and adequately mixed in a proportion of 95 volume % and 5 volume %, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000 °C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 5 volume % of CaTiO₃ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indentor, such a high hardness was given as represented by 7800 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.4 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1300 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Example 10)

Example 9 was repeated except using 5 volume % of MgTiO₃ as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained MgTiO₃ and had a similar hardness, toughness and heat resistance to those of Example 9.

(Example 11)

Example 9 was repeated except using 5 volume % of SrTiO₃ as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained SrTiO₃ and had a similar hardness, toughness and heat resistance to those of Example 9.

(Example 12)

Example 9 was repeated except using 5 volume % of LiTiO₃ as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained LiTiO₃ and had a similar hardness, toughness and heat resistance to those of Example 9.

(Example 13)

Example 9 was repeated except using a mixture of CaO and TiO₂ in a volume ratio of 1 : 1 as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained CaTiO₃ and had a similar hardness, toughness and heat resistance to those of Example 9.

(Example 14)

Example 9 was repeated except using a mixture of MgO and TiO₂ in a volume ratio of 1 : 1 as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained MgTiO₃ and had a similar hardness, toughness and heat resistance to those of Example 9.

(Example 15)

CaTiO₃ was used as a sintering agent. A synthetic diamond powder with an average grain diameter of 15 µm and CaTiO₃ powder with a grain diameter of 1 ∼ 2 µm were respectively shaped in plates with a thickness of 2 mm and lmm, alternately laminated, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000°C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 2 volume % of CaTiO₃ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by about 8100 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.5 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1300 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Example 16)

CaTiO₃ was used as a sintering agent. A plate-shaped sintered compact of a high purity isotropic graphite with an average grain diameter of 3 µm, having a thickness of 2 mm, and a molded and shaped body of CaTiO₃ powder with a grain diameter of 1 to 2 µm, having a thickness of 1 mm, were alternately laminated, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000 °C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Girdle type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 3 volume % of CaTiO₃ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by about 7800 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.3 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1300 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Comparative Example 3)

CaTiO₃ was used as a sintering agent. Example 9 was repeated except adding a micro amount (about 0.05 volume %) of CaTiO₃ powder with a grain diameter of 1 to 2 µm to a synthetic diamond powder with an average grain diameter of 3.5 µm and adequately mixing them to prepare a raw material, thus obtaining a diamond sinterd compact therefrom. However, the thus obtained sintered compact contained more non-sintered parts.

(Comparative Example 4)

CaTiO₃ was used as a sintering agent. Example 9 was repeated except adding 60 volume % of a synthetic diamond powder with an average grain diameter cf 3.5 µm and 40 volume % of CaTiO₃ powder with a grain diameter of 1 to 2 µm and adequately mixing them to prepare a raw material, thus obtaining a diamond sinterd compact therefrom. In the thus obtained sintered compact, however, the grains were not sufficiently bonded with each other to give a low hardness, i.e. about 3500 kg/mm².

(Example 17)

Y₂TiO₅ was used as a sintering agent. A synthetic diamond powder with an average grain diameter of 3.5 µm and Y₂TiO₅ powder with a grain diameter of 1 ∼ 2 µm were respectively and adequately mixed in a proportion of 95 volume % and 5 volume %, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000 °C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 5 volume % of Y₂TiO₅ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indentor, such a high hardness was given as represented by 7800 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.4 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1200 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Example 18)

Example 17 was repeated except using 5 volume % of La₂Ti₂O₇ as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained La₂Ti₂O₇ and had a similar hardness, toughness and heat resistance to those of Example 17.

(Example 19)

Example 17 was repeated except using 5 volume % of Ce₂TiO₅ as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained Ce₂TiO₅ and had a similar hardness, toughness and heat resistance to those of Example 17.

(Example 20)

Example 17 was repeated except using a mixture of Y₂O₃ and TiO₂ in a volume ratio of 1 : 1 as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained a composite oxide of Y₂O₃ and TiO₂ and had a similar hardness, toughness and heat resistance to those of Example 17.

(Example 21)

Example 17 was repeated except using a mixture of CeO₂ and TiO₂ in a volume ratio of 1 : 1 as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained a composite oxide of CeO₂ and TiO₂ and had a similar hardness, toughness and heat resistance to those of Example 17.

(Example 22)

Example 17 was repeated except using a mixture of La₂O₃ and TiO₂ in a volume ratio of 1 : 2 as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained a composite oxide of La₂O₃ and TiO₂ and had a similar hardness, toughness and heat resistance to those of Example 17.

(Example 23)

Y₂TiO₅ was used as a sintering agent. A synthetic diamond powder with an average grain diameter of 15 µm and Y₂TiO₅ powder with a grain diameter of 1 ∼ 2 µm were respectively shaped in plates with a thickness of 2 mm and lmm, alternately laminated, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000°C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 2 volume % of Y₂TiO₅ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by about 8000 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.4 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1200 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Example 24)

Example 23 was repeated except using a mixture of CeO₂ and TiO₂ in a volume ratio of 1 : 1 as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained a composite oxide of CeO₂ and TiO₂ and had a similar hardness, toughness and heat resistance to those of Example 23.

(Example 25)

Y₂TiO₅ was used as a sintering agent. A plate-shaped sintered compact of a high purity isotropic graphite with an average grain diameter of 3 µm, having a thickness of 2 mm, and a molded and shaped body of Y₂TiO₅ powder with a grain diameter of 1 to 2 µm, having a thickness of 1 mm, were alternately laminated, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000 °C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 3 volume % of Y₂TiO₅ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by about 7800 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.3 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1200 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Comparative Example 5)

Y₂TiO₅ was used as a sintering agent. Example 17 was repeated except adding a micro amount (about 0.05 volume %) of Y₂TiO₅ powder with a grain diameter of 1 to 2 µm to a synthetic diamond powder with an average grain diameter of 3.5 µm and adequately mixing them to prepare a raw material, thus obtaining a diamond sinterd compact therefrom. However, the thus obtained sintered compact contained more non-sintered parts.

(Comparative Example 6)

Y₂TiO₅ was used as a sintering agent. Example 17 was repeated except adding 60 volume % of a synthetic diamond powder with an average grain diameter of 3.5 µm and 40 volume % of Y₂TiO₅ powder with a grain diameter of 1 to 2 µm and adequately mixing them to prepare a raw material, thus obtaining a diamond sinterd compact therefrom. In the thus obtained sintered compact, however, the grains were not sufficiently bonded with each other to give a low hardness. i.e. about 3500 kg/mm².

(Example 26)

CaSiO₃ was used as a sintering agent. A synthetic diamond powder with an average grain diameter of 3.5 µm and CaSiO₃ powder with a grain diameter of 1 ∼ 2 µm were respectively and adequately mixed in a proportion of 95 volume % and 5 volume %, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000 °C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 5 volume % of CaSiO₃ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by 7600 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.4 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1200 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Example 27)

Example 26 was repeated except using 5 volume % of Mg₂Si₃O₈ as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained Mg₂Si₃O₈ and had a similar hardness, toughness and heat resistance to those of Example 26.

(Example 28)

Example 26 was repeated except using 5 volume % of BaSiO₃ as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained BaSiO₃ and had a similar hardness, toughness and heat resistance to those of Example 26.

(Example 29)

Example 26 was repeated except using a mixture of CaO and SiO₂ in a volume ratio of 1 : 1 as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained a composite oxide of CaO and SiO₂ and had a similar hardness, toughness and heat resistance to those of Example 26.

(Example 30)

Example 26 was repeated except using a mixture of MgO and SiO₂ in a volume ratio of 2 : 3 as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained a composite oxide of MgO and SiO₂ and had a similar hardness, toughness and heat resistance to those of Example 26.

(Example 31)

CaSiO₃ was used as a sintering agent. A synthetic diamond powder with an average grain diameter of 15 µm and CaSiO₃ powder with a grain diameter of 1 ∼ 2 µm were respectively shaped in plates with a thickness of 2 mm and lmm, alternately laminated, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000°C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 2 volume % of CaSiO₃ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by about 7800 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.5 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1200 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Example 32)

Example 31 was repeated except using a mixture of CaO and SiO₂, each having a grain diameter of 1 to 2 µm, in a volume ratio of 1 : 1 as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact comtained a composite oxide of CaO and SiO₂ and had a similar hardness, toughness and heat resistance to those of Example 31.

(Example 33)

CaSiO₃ was used as a sintering agent. A plate-shaped sintered compact of a high purity isotropic graphite with an average grain diameter of 3 µm , having a thickness of 2 mm, and a molded and shaped body of CaSiO₃ powder with a grain diameter of 1 to 2 µm, having a thickness of 1 mm, were alternately laminated, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000 °C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 3 volume % of CaSiO₃ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by about 7500 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.3 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1200 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Comparative Example 7)

CaSiO₃ was used as a sintering agent. Example 26 was repeated except adding a micro amount (about 0.05 volume %) of CaSiO₃ powder with a grain diameter of 1 to 2 µm to a synthetic diamond powder with an average grain diameter of 3.5 µm and adequately mixing them to prepare a raw material, thus obtaining a diamond sinterd compact therefrom. However, the thus obtained sintered compact contained more non-sintered parts.

(Comparative Example 8)

CaSiO₃ was used as a sintering agent. Example 26 was repeated except adding 60 volume % of a synthetic diamond powder with an average grain diameter of 3.5 µm and 40 volume % of CaSiO₃ powder with a grain diameter of 1 to 2 µm and adequately mixing them to prepare a raw material, thus obtaining a diamond sinterd compact therefrom. In the thus obtained sintered compact, however, the grains were not sufficiently bonded with each other to give a low hardness, i.e. about 3500 kg/mm².

(Example 34)

Y₂SiO₅ was used as a sintering agent. A synthetic diamond powder with an average grain diameter of 3.5 µm and Y₂SiO₅ powder with a grain diameter of 1 ∼ 2 µ m were respectively and adequately mixed in a proportion of 95 volume % and 5 volume %, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000 °C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 5 volume % of Y₂SiO₅ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by 7200 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.3 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1200 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Example 35)

Example 34 was repeated except using 5 volume % of La₂Si₂O₇ as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained La₂Si₂O₇ and had a similar hardness, toughness and heat resistance to those of Example 34.

(Example 36)

Example 34 was repeated except using 5 volume % of Ce₂SiO₅ as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained Ce₂SiO₅ and had a similar hardness, toughness and heat resistance to those of Example 34.

(Example 37)

Example 34 was repeated except using a mixture of Y₂O₃ and SiO₂ in a volume ratio of 1 : 1 as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained a composite oxide of Y₂O₃ and SiO₂ and had a similar hardness, toughness and heat resistance to those of Example 34.

(Example 38)

Example 34 was repeated except using a mixture of CeO₂ and SiO₂ in a volume ratio of 1 : 1 as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained a composite oxide of CeO₂ and SiO₂ and had a similar hardness, toughness and heat resistance to those of Example 34.

(Example 39)

Example 34 was repeated except using a mixture of La₂O₃ and SiO₂ in a volume ratio of 1 : 2 as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained a composite oxide of La₂O₃ and SiO₂ and had a similar hardness, toughness and heat resistance to those of Example 34.

(Example 40)

Y₂SiO₅ was used as a sintering agent. A synthetic diamond powder with an average grain diameter of 15 µm and Y₂SiO₅ powder with a grain diameter of 1 ∼ 2 µ m were respectively shaped in plates with a thickness of 2 mm and lmm, alternately laminated, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000°C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 2 volume % of Y₂SiO₅ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by about 7600 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.4 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1200 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Example 41)

Example 40 was repeated except using a mixture of CeO₂ and SiO₂, each having a grain diameter of 1 to 2 µ m, in a volume ratio of 1 : 1 as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained a composite oxide of CeO₂ and SiO₂ and had a similar hardness, toughness and heat resistance to those of Example 40.

(Example 42)

Y₂SiO₅ was used as a sintering agent. A plate-shaped sintered compact of a high purity isotropic graphite with an average grain diameter of 3 µm , having a thickness of 2 mm, and a molded and shaped body of Y₂SiO₅ powder with a grain diameter of 1 to 2 µm, having a thickness of 1 mm, were alternately laminated, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000 °C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 3 volume % of Y₂SiO₅ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by about 7500 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.2 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1200 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Comparative Example 9)

Y₂SiO₅ was used as a sintering agent. Example 34 was repeated except adding a micro amount (about 0.05 volume %) of Y₂SiO₅ powder with a grain diameter of 1 to 2 µm to a synthetic diamond powder with an average grain diameter of 3.5 µm and adequately mixing them to prepare a raw material, thus obtaining a diamond sinterd compact therefrom. However, the thus obtained sintered compact contained more non-sintered parts.

(Comparative Example 10)

Y₂SiO₅ was used as a sintering agent. Example 34 was repeated except adding 60 volume % of a synthetic diamond powder with an average grain diameter of 3.5 µm and 40 volume % of Y₂SiO₅ powder with a grain diameter of 1 to 2 µm and adequately mixing them to prepare a raw material, thus obtaining a diamond sinterd compact therefrom. In the thus obtained sintered compact, however, the grains were not sufficiently bonded with each other to give a low hardness, i.e. about 3500 kg/mm².

(Example 43)

A mixture of SiO₂ and TiO₂ with a grain diameter of 1 to 2 µm in a proportion of 3 : 2 (TiO₂ 40 volume %) was used as a sintering agent. A synthetic diamond powder with an average grain diameter of 3.5 µm and a powder of the above described mixture were respectively and adequately mixed in a proportion of 95 volume % and 5 volume %, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000°C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 5 volume % of a composite oxide of SiO₂ and TiO₂, in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by 6800 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.3 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1200 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Example 44)

Example 43 was repeated except adjusting the mixing ratio of SiO₂ and TiO₂ to 5 : 1 by volume to prepare a diamond sintered compact. The thus obtained sintered compact contained a composite oxide of SiO₂ and TiO₂ and had a similar hardness, toughness and heat resistance to those of Example 43.

(Example 45)

Example 43 was repeated except using a mixture of silicic anhydride (H₃SiO₃) and TiO₂ in a proportion of 2 : 1 by volume as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained a composite oxide of SiO₂ and TiO₂ and had a similar hardness, toughness and heat resistance to those of Example 43.

(Example 46)

Example 43 was repeated except using a mixture of orthosilicic acid (H₄SiO₄) and TiO₂ in a proportion of 3 : 1 by volume as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained a composite oxide of SiO₂ and TiO₂ and had a similar hardness, toughness and heat resistance to those of Example 43.

(Example 47)

A mixture of SiO₂ and TiO₂ with a grain diameter of 1 to 2 µm in a proportion of 3 : 2 by volume was used as a sintering agent. A synthetic diamond powder with an average grain diameter of 15 µm and a powder of the above described mixture were respectively shaped in plates with a thickness of 2 mm and 1 mm, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000 °C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 2 volume % of a composite oxide of SiO₂ and TiO₂, in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by 7200 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.4 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1200 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Example 48)

Example 47 was repeated except using a mixture of silicic anhydride (H₃SiO₃) and TiO₂ in a proportion of 2 : 1 by volume as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained a composite oxide of SiO₂ and TiO₂ and had a similar hardness, toughness and heat resistance to those of Example 47.

(Example 49)

A mixture of SiO₂ and TiO₂ in a proportion of 3 : 2 by volume was used as a sintering agent. A plate-shaped sintered compact of a high purity isotropic graphite with an average grain diameter of 3 µm , having a thickness of 2 mm, and a molded and shaped body of the above described mixed powder, having a thickness of 1 mm, were alternately laminated, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000 °C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 3 volume % of a composite oxide of SiO₂ and TiO₂ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by about 7000 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.2 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1200 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Comparative Example 11)

A mixture of SiO₂ and TiO₂ in a proportion of 3 : 2 by volume was used as a sintering agent. Example 43 was repeated except adding a micro amount (about 0.05 volume %) of a powder of the above described mixture to a synthetic diamond powder with an average grain diameter of 3.5 µm and adequately mixing them to prepare a raw material, thus obtaining a diamond sinterd compact therefrom. However, the thus obtained sintered compact contained more non-sintered parts.

(Comparative Example 12)

A mixture of SiO₂ and TiO₂ in a proportion of 3 : 2 by volume was used as a sintering agent. Example 43 was repeated except adding 60 volume % of a synthetic diamond powder with an average grain diameter of 3.5 µm and 40 volume % of a powder of the above described mixture and adequately mixing them to prepare a raw material, thus obtaining a diamond sinterd compact therefrom. In the thus obtained sintered compact, however, the grains were not sufficiently bonded with each other to give a low hardness, i.e. about 3500 kg/mm².

(Comparative Example 13)

Example 43 was repeated except using only SiO₂ as a sintering agent to prepare a diamond sintered compact. However, the thus obtained sintered compact contained more non-sintered parts.

(Comparative Example 14)

Example 43 was repeated except using only TiO₂ as a sintering agent to prepare a diamond sintered compact. However, the thus obtained sintered compact contained more non-sintered parts.

(Comparative Example 15)

Example 43 was repeated except using only silicic anhydride as a sintering agent to prepare a diamond sintered compact. However, the thus obtained sintered compact contained more non-sintered parts.

(Example 50)

Fe₂SiO₄ was used as a sintering agent. A synthetic diamond powder with an average grain diameter of 3.5 µm and Fe₂SiO₄ powder with a grain diameter of 1 ∼ 2 µm were respectively and adequately mixed in a proportion of 95 volume % and 5 volume %, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000 °C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 5 volume % of Fe₂SiO₄ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by 8100 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.4 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1200 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.

(Example 51)

Example 50 was repeated except using a mixture of FeO and SiO₂ in a mole ratio of 2 : 1 as a sintering agent to prepare a diamond sintered compact. The thus obtained sintered compact contained Fe₂SiO₄ and had a similar hardness, toughness and heat resistance to those of Example 50.

(Example 52)

Fe₂SiO₄ was used as a sintering agent. A synthetic diamond powder with an average grain diameter of 15 µm and Fe₂SiO₄ powder with a grain diameter of 1 ∼ 2 µm were respectively shaped in plates with a thickness of 2 mm and 1 mm, alternately laminated, charged in a Mo capsule, and maintained and sintered at pressure and temperature conditions of 7.5 GPa and 2000°C for 15 minutes using an ultra-high pressure and high temperature producing apparatus of Belt type. The resulting diamond sintered compact was subjected to identification of the composition by X-ray diffraction to detect about 2 volume % of Fe₂SiO₄ in addition to diamond.
When the hardness of the sintered compact was estimated by a Knoop indenter, such a high hardness was given as represented by about 8300 kg/mm². When the resulting sintered compact and commercially available Co-binder compact were compared as to the fracture toughness by the indentation method, the former gave a relative toughness of about 1.4 times as large as that of the prior art compact (the latter). When the resulting sintered compact was heat-treated in vacuum at 1200 °C and then subjected to measurement of the hardness and toughness, there was found little change from before the heat treatment. In addition, there was no deterioration of the sintered compact by a treatment with an acid.
As illustrated above, the diamond sintered compact of the present invention has a higher strength and better heat, breakage and corrosion resistance than the compacts of the prior art, and can thus be effectively applied to tool materials for cutting or polishing non-ferrous metals or ceramics, and to edge materials for drill bits for petroleum excavation.

Claims

A diamond sintered compact comprising:
(a) in the range of from 0.1 to 30 volume % of at least one compound which comprises oxygen and at least one element selected from silicon and titanium; and

(b) the balance of diamond.
A diamond sintered compact as claimed in claim 1, wherein the diamond is a powder with a grain diameter in the range of from 0.01 to 200 µm.
A process for the production of a diamond sintered compact as claimed in claim 1 or claim 2, comprising using, as a sintering agent, a powder of at least one compound which comprises oxygen and at least one element selected from silicon and titanium, mixing the powder with diamond powder, non-diamond carbon powder or mixed powders of diamond and non-diamond carbon, and maintaining and sintering the resulting mixture under pressure and temperature conditions in the thermodynamically stable region of diamond.
A process for the production of a diamond sintered compact as claimed in claim 3, wherein the sintering agent has a grain size in the range of from 0.01 to 10 µm.
A diamond sintered compact as claimed in claim 1 or claim 2, wherein the said at least one compound comprises oxygen and titanium and either at least one metal selected from iron, cobalt, nickel and manganese or at least one metal selected from the alkali metals and the alkaline earth metals or at least one metal selected from the rare earth elements.
A diamond sintered compact as claimed in claim 5, wherein the said at least one compound comprises a titanate of the said at least one metal.
A diamond sintered compact as claimed in claim 5, wherein the said at least one compound comprises a composite oxide or solid solution consisting of titanium oxide and an oxide of the said at least one metal.
A process for the production of a diamond sintered compact as claimed in any one of claims 5 to 7, which comprises using, as a sintering agent, a titanate of either at least one metal selected from iron, cobalt, nickel and manganese or at least one metal selected from the alkali metals and the alkaline earth metals or at least one metal selected from the rare earth elements, mixing a powder of the titanate with diamond powder, non-diamond carbon powder or mixed powders of diamond and non-diamond carbon, and maintaining and sintering the resulting mixture under pressure and temperature conditions in the thermodynamically stable region of diamond.
A process for the production of a diamond sintered compact as claimed in any one of claims 5 to 7, which comprises using, as a sintering agent, either titanium oxide and a titanate of at least one metal selected from iron, cobalt, nickel and manganese or a titanate of at least one metal selected from the alkali metals and the alkaline earth metals or a titanate of at least one metal selected from the rare earth elements, laminating a shaped body of a powder of the titanate and a shaped body of diamond powder, shaped body of non-diamond carbon powder or shaped body of mixed powders of diamond and non-diamond carbon, and maintaining and sintering the resulting laminate under pressure and temperature conditions in the thermodynamically stable region of diamond.
A process for the production of a diamond sintered compact as claimed in claim 8 or claim 9, wherein a mixture comprising titanium oxide and an oxide of either at least one metal selected from iron, cobalt, nickel and manganese or at least one metal selected from the alkali metals and the alkaline earth metals or at least one metal selected from the rare earth elements is used as the sintering agent in place of the titanate.
A diamond sintered compact as claimed in claim 1 or claim 2, wherein the said at least one compound comprises silicon, oxygen and either an alkaline earth metal or a rare earth element.
A diamond sintered compact as claimed in claim 11, wherein the said at least one compound comprises a silicate of an alkaline earth metal or a silicate of a rare earth element.
A diamond sintered compact as claimed in claim 11, wherein the said at least one compound comprises a composite oxide or solid solution consisting of silicon oxide and an oxide of either an alkaline earth metal or a rare earth element.
A process for the production of a diamond sintered compact as claimed in any one of claims 11 to 13, which comprises using, as a sintering agent, a silicate of an alkaline earth metal or a silicate of a rare earth element, mixing a powder of the silicate with diamond powder, non-diamond carbon powder or mixed powders of diamond and non-diamond carbon, and maintaining and sintering the resulting mixture under pressure and temperature conditions in the thermodynamically stable region of diamond.
A process for the production of a diamond sintered compact as claimed in any one of claims 11 to 13, which comprises using, as a sintering agent, a silicate of an alkaline earth metal or a silicate of a rare earth element, laminating a shaped body of a powder of the silicate and a shaped body of diamond powder, shaped body of non-diamond carbon powder or shaped body of mixed powders of diamond and non-diamond carbon, and maintaining and sintering the resulting laminate under pressure and temperature conditions in the thermodynamically stable region of diamond.
A process for the production of a diamond sintered compact as claimed in claim 14 or 15, wherein a mixture of silicon oxide and an oxide of either an alkaline earth metal or a rare earth element is used as the sintering agent in place of the silicate.
A diamond sintered compact as claimed in claim 1 or claim 2, wherein the said at least one compound comprises silicon, titanium and oxygen.
A diamond sintered compact as claimed in claim 17, wherein the said at least one compound comprises a composite oxide or solid solution consisting of silicon oxide and titanium oxide.
A process for the production of a diamond sintered compact as claimed in claim 17 or claim 18, which comprises using, as a sintering agent, a mixture of silicon oxide and titanium oxide, mixing a powder of the mixture with diamond powder, non-diamond carbon powder or mixed powders of diamond and non-diamond carbon, and maintaining and sintering the resulting mixture under pressure and temperature conditions in the thermodynamically stable region of diamond.
A process for the production of a diamond sintered compact as claimed in claim 17 or claim 18, which comprises using a mixture of silicon oxide and titanium oxide, laminating a shaped body of a powder of the mixture and a shaped body of diamond powder, shaped body of non-diamond carbon powder or shaped body of mixed powders of diamond and non-diamond carbon, and maintaining and sintering the resulting laminate under pressure and temperature conditions in the thermodynamically stable region of diamond.
A process for the production of a diamond sintered compact as claimed in claim 18 or claim 19, wherein the mixture of silicon oxide and titanium oxide used as the sintering agent contains the titanium oxide in a proportion in the range of from 0.1 to 50 volume %.
A process for the production of a diamond sintered compact as claimed in any one of claims 19 to 21, wherein the silicon oxide contained in the mixture of silicon oxide and titanium oxide used as the sintering agent is silicic acid or silicon oxide hydrate.